Abstract

We present measurements of the frequency shift of the Rb electron-paramagnetic-resonance (EPR) line in the presence of nuclear-polarized 3He gas for the temperature range of 30 to 85 °C. The frequency shift is due to the Fermi-contact interaction between the Rb valence electron and the polarized 3He nucleus. Expressions for both the frequency shift and the spin-exchange cross section are derived in terms of the strength of this contact interaction. From these expressions and the measured frequency shift, we estimate the Rb-3He spin-exchange cross section. The Rb EPR frequency shift, which is 53 kHz for a 100% polarized 10-amagat 3He sample at 50 °C, can be used to determine the absolute polarization of nuclear polarized 3He targets. From these measurements, one can also predict the shift of the 3He NMR line due to a polarized Rb vapor.